“Dual-fuel engines” are internal combustion engines configured to operate on both a gaseous fuel and diesel fuel simultaneously. The typical gaseous fuel used in dual-fuel engines is natural gas. However, other gaseous fuels such as propane or hydrogen could be used.
In a dual-fuel engine, the diesel fuel is important for ignition; it auto ignites under compression and its combustion ignites the natural gas. The use of natural gas to replace a significant portion of the fuel energy provided by diesel fuel contributes to lowered emissions and operating costs.